Cash played for Northside Little League in Tampa, Florida when they made it to the Little League World Series in 1989. Cash played college baseball for the Florida State University Seminoles under head coach Mike Martin. He batted and threw right-handed. While at FSU, Cash started 148 games as an infielder. Cash batted .299 with a career OPS of .923.[1] He also appeared in two College World Series (1998, 1999) for Florida State, including a second-place finish in 1999. In 1999 Kevin Cash was voted as a second-team All American at third base by NCBWA.[2] After going undrafted in 1999, he played for the Falmouth Commodores of the Cape Cod Baseball League. When both the team's primary catchers suffered injuries that summer, he volunteered to convert to catcher and went on to earn team MVP honors. In August, he signed with the Toronto Blue Jays as an undrafted free agent.[3]

On November 2, 2007, Cash opted for free agency after refusing to accept an outright assignment to AAA Pawtucket. On December 13, 2007, Cash re-signed with the Red Sox to a minor league contract and an invitation to spring training.

On March 25, 2008, Cash's contract was purchased. He acted as the personal catcher for knuckleball pitcher Tim Wakefield after Doug Mirabelli left the Sox. He was also notable for wearing his plastic catcher's cap forward (similar to how a field player wears a normal baseball cap) under his mask; normally, catchers will turn the cap around to provide stability for their mask. In Boston, Cash wore the uniform number 36, except from August 16, 2008 to the end of the 2008 season, due to Paul Byrd's joining the Red Sox and wearing his customary number 36. During this period, Cash switched to number 30. On December 12, 2008, Cash was non-tendered by the Red Sox, officially making him a free agent.[5]

On December 23, 2008, Cash signed a minor league deal with the New York Yankees with an invitation to Spring Training.[6] He began the 2009 season with the Triple-A Scranton/Wilkes-Barre Yankees. On May 8, Cash was called up due to injuries to both Jorge Posada and José Molina. He was optioned to AAA Scranton on May 29 and was placed on the injured reserve list after undergoing surgery to repair a torn rotator .

Released by the New York Yankees' organization on September 5, 2009, Cash announced his retirement from baseball. However, he soon changed his mind, and on January 22, 2010, Cash signed a minor league contract with the Houston Astros.

On May 5, 2010, Cash was called up to the Astros to replace a struggling J. R. Towles. He had 11 hits in 54 at bats with Houston.

On July 1, 2010, Cash was acquired by the Red Sox for Ángel Sánchez after Jason Varitek went on the disabled list. As the backup catcher for the Red Sox for part of the season, he had 60 at bats and a .133 batting average, compiling just eight hits with the team. He finished the year with .167 average (AL and NL stats combined). He refused a minor league assignment on October 12, and became a free agent. He signed a minor-league contract with the Texas Rangers on November 11, 2010, and played the entire 2011 season at their Triple-A affiliate in Round Rock.

On December 5, 2014, the Tampa Bay Rays hired Cash as their manager, succeeding Joe Maddon.[10] In 2015 he was successful on a lower percentage of replay challenges than any other MLB manager with 10 or more challenges, at 31.5%.[11]